Fighting Bowden Cable Ooze

Is there a way to fight oozing when raising the Z axis? I'm using Slic3r and Pronterface. I can't seem to find a way to speed up my Z axis. As you can see in the picture of a sphere, I get a ridge where the Z axis raises each time. Then I get a little bumpe when ever it raises elsewhere. Is it possible to fix this some how or is this just life with a bowden cable?

Increase your z speed if possible and/or z acceleration and/or z jerk in Marlin. You also want your retract really fast and not too short or long (too long causes the head to stop for a long time just before the Z move). Last but not least if you are trying to print a hollow part (which it appears) try actually printing with 0.01 infill insteadas it makes the head go in for the infill before doing the Z move.

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in slic3r have you increased retraction distance. i think default is 3mm, maybe try 20mm? it will slow down your print, but may stop extra ooze.

Something like that anyway. Ive been playing around with repetier host and slic3r. If the slic3r settings are the same, then the retraction rate is on the lower left side of configuration screen.

I'm using sprinter firmware, I should mention.

I have my retraction at 5mm at 150mm/s which is probably as fast as I can go. This cuts down on it significantly, but it is still there.

I don't want to increase by retraction by much more since, like mentioned earlier, my hotend sits still and oozes while it retracts.

Does the retraction happen during Z axis movements as well as X and Y? Like if I set my minimum travel to less than the layer height, when the Z moves to the next layer, will I get retraction?

I would think 150mm/s is way faster than you can go, so perhaps why it doesn't work. Try 15mm/s.

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5mm of retraction is to much. Try 1.5 - 3.5mm. The speed setting can remain at 150mm/s because acceleration means it will never reach that speed and you should also have the actual top speed limited in the firmware.

Most important is the Z speed. My Z speed is set to 15mm/s (firmware limit) which is really fast (default is like 2mm/s) and my Z moves never leave a mark. You can also try turning down your temp by a couple degrees.

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One other possible suggestion (and the big thing I'm waiting for before I go back to experimenting with bowden extruders) is the Matthew Roberts advance algorithm which currently is partially supported by the Marlin firmware.

It basically introduces spring/pressure modelling into the e axis. It's useful with non-bowden designs, and IMO essential for bowden designs. I don't know what the state of the support in marlin is, but I strongly feel that it's the direction that our stepper extruder controllers need to go.

Maybe the support in marlin today is half-baked (like I said, haven't tried it yet) and this doesn't help you solve the problems you're having today... but something to keep an eye out for if you're set on using a bowden extruder. Either way, if you're comfortable configuring your firmware it's certainly worth a try.

I took everyone's advice and am now getting good results.

Set up:

Techzone Huxley
J-Head Hotend (Awsome BTW)
DIY Nichrome Wire Heated bed
RAMPS 1.4 with Marlin

Slic3r/SFACT (Depepding on the part. Slic3r is fast but tends to exclude thin parts. SFACT seems to take days to slice but it much more thorough.)

Pronterface

I've realized that the ooze left behind during Z changes was a bigger issue than the stringing. I changed by retraction back to 1.2mm in 11.8 mm/sec (can't go any faster). This dramatically cut back on the amount extrusion left during z changes. I've also increased my over all print speed which helped as well, thanks to Marlin.

Ironically, I don't see as much stringing as I thought I would even with the limited retraction.

The biggest improvement came by using SFACT's Jitter and Clip functions. I won't go into detail on them, but for anyone else having similar problems as mine, I would suggest getting SFACT and playing around with it.

I think its almost time for me to graduate to the full Skeinforge. Thanks for all the help!